Plywood board and process of making the same



Sept. 13, 1932. SATQW I 1,877,202

PLYWOOD BOARD AND PROCESS OF MAKING THE SAME Filed April 24, 1930gnvenboz his au mqs.

Patented Sept. 13, 1932 UNITED STATES PATENT OFFICE TEIKICHI SATOW, OFTOKYO, JAPAN Application filed April 24, 1930. Serial No. 447,038.

This invention relates to a novel composite board product and process ofmaking the same.

The object of my invention is to produce a composite or plywood boardconsisting of a plurality of sheets secured together in flat- Wiserelation by the useof dry glue and the application of heat and pressure.

A further object is to produce a composite board of the nature referredto, in a most simple, efficient, expeditious and economical manner, andwhether soft or hard wood sheets are employed.

Other objects of the invention will appear more fully hereinafter.

The invention consists substantially in the steps, mode of procedure,operations, and product, hereinafter more fully set forth, and finallypointed out in the appended claims.

Referring to the drawing,

Figure 1 is an elevational view of the plywood board of this invention.

Fig. 2 is a top plan with each layer broke away.

Heretofore in the manufacture of composite boards, panels or the like,it has been the practice to steam the stock wood, to soften it, then toslice the same, while so softened, into thin sheets, then to dry thesheets, then to apply glue in a wet condition to one or both surfaces ofa plurality of said sheets and to pile them flatwise upon each other andfinally to dry the assembled pile.

This operation is objectionable for several reasons. In the first placetwo drying operations are required, one after the stock wood is steamed,as glue will not adhere to the surface of a wet sheet, and another afterthe application of the wet glue. Again, after the wet glue is applied itis necessary to retain the assembled sheets under pressure for a sufii-'cient length of time to enable the glue to set. This requires at leastsix hours and sometimes much longer. This necessitates a large area ofspace if the production is of any consequential volume, and reduces thecapacity output and efficient operation of the factory. In addition,where the wet glue method is employed, the glue must be maintainedduring working hours in a fluid state to enable it to be properlyapplied, and if any excess of glue remains at night it becomes set andhard over night and cannot be used the next day. This entails a seriouswaste and loss. Again, in the use of the wet glue process the sheets orpanels must be applied together quickly after the glue has been appliedto them, otherwise the glue will lose its binding power, therebyresulting in a failure to secure the desired degree of adherence of theboards or sheets. Finally, panels or boards built up by thin sheetssecured together by means of wet glue are not efficiently waterproof.That is, while they may be able to resist the penetration of water whenboiled for a few hours, or when steeped in water for a day or two,nevertheless they are unable to retain their waterproof quality for ayear or more. These are some of the serious objections which areencountered by present methods of making composite boards, and whichresult in great loss and expense. I

It is among the special purposes of my present invention to obviatethese and many other difficulties attendant upon the use of the wet glueprocess of making up composite boards from thin sheets of wood.

In carrying out my invention, I propose to employ a glue product havingadhesion and waterproofing qualities and of such nature as to enable itto be applied and used in the dry state, and pressing together thesheets to which it has been applied by means of hot presses. To this endI propose to employ a dry glue product which is thermoplastic.

The thin wood veneers or sheets are prepared by steaming the stock, asbefore, and slicing the steamed and softened stock into thin sheets,which are then dried, but with this difference. Instead of extractingthe moisture by drying till not more than two percent (2%) remains inthe sheets, as heretofore required with the wet process, the drying inpreparation for utilization of my process need be carried on to thepoint of leaving from 10% to 15% moisture in the sheets. This greatlyreduces the cost and time of preparing the sheets. The dry glue is thenapplied and spread over the surfaces layers extends at right angles.

of. the sheets and the sheets are stacked or.

This may be accomplished either by hydraulic.

hot presses, or by heated rollers. Instead of the six or more hoursheretofore required in this step of. operation with the wet process itrequires less than five minutes with the dry process of my invention,generally only about one minute. This attains an enormous advantage insaving time and expense, and results in the roduction of an eiiicientlywaterproofed nished product, the conservation of factory space and acontinuous production, particularly where heated rollers are employed.It also results in the production of eiiicient uniform quality ofcomposite board products whether soft wood or hard wood sheets beemployed, whereas with the wet glue process a difference in quality ofthe composite board product is caused according to whether the sheetsare of hard wood or of soft wood.

A plywood board made in accordance with this invention is clearly shownin the figures. As depicted the board is made up of four plies of thinwood veneers or sheets 1, 2, 3 and 4: and bound together by very thinlayers of glue 5. As shown, the wood layers are arranged so that theirgrain in adjacent Of course, the board may consist of any desired numberof layers from two upwards.

It is essential, in accordance with my invention, not only that the dryglue material used shall be thermoplastic, but also that it shall have astrongly binding power and shall be of waterproof character. Any gluesubstance which possesses these characteristics of being thermoplastic,waterproof and having strongly binding power is suitable for use incarrying out my invention.

I have found that vegetable proteidal substances, such as soyabeanproteid, or animal proteid substances, such as casein, or blood, whentreated with an active methylene compound, as well as synthetic resinssuch as phenol condensation products, or urea condensation products, ora combination of such proteidal and condensation products may well servethe purposes of my invention. In practice, thercombination of theproteidal and condensation products is preferable not only because it ismore economical, but also it is more efiicient since it utilizes to bestadvantage the increased and predominating binding power of the proteidalsubstancesv and the increased predominating waterproofingcharacteristics of the condensation products. Moreover, when thecombined products are employed the proteidal part forms a very thincoating on the wood surface which prevents or retards the absorption ofthe condensation product into the wood tissues, which would beobjectionable proteidal substances indurated with an active methylenecompound.

To, say, 100 pounds of soya bean meal is added a few pounds of dilutedsolution of ammonia or caustic soda, to serve as a glutinizmg agenttherefor. To this mass is added from 5 to 15 pounds of beta naphthol orits sodium salt to impart a desirably high degree of thermo plasticitythereto. Then I add from 8 to 15 pounds of formaldehyde solution or itsequivalent. The whole mass is then thoroughly kneaded into homogeneityand is finally dried into powder form.

Or, to say, 100 pounds of soya bean meal and 5 to 10 pounds of blood,mixed together, I add 10 pounds of sodium triphosphate and 10 to 15pounds of calcium hydroxid, and 10 pounds of copper sulphate. In thiscase the sodium tri-phosphate glutinizes the mass and the calciumhydroxid and copper sulphate act as condensing agents. The mass isthoroughly mixed in powder form.

Instead of using the soya bean meal its extracted refined proteid may beused.

Instead of blood, casein may be used.

The wood sheets are prepared in the usual Way except that they may andpreferably should contain from 10% to 13% moisture. The surfaces of thewood sheets which are to receive the dry powdered glue product arepreferably slightly moistened by wiping the same with a dampened cloth,or otherwise, as may be convenient. If desired this moistening may bereadily accomplished either by hand or by passing the sheets betweenrolls covered with. a dampened cloth. To the dampened wood surface thedry glue powder is applied in any suitable or convenient way, as, forinstance, by passing the dampened board through a box in which thepowdered glue material is maintained in a flying whirl by means of anair blast. Thus a thin film of the glue material is applied to thedampened surface of the wood sheets. Of course, many other methods ofapplying the dry powdered glue material may be employed.

The panels after receiving the dry glue material are then stacked orpiled upon each other in the desired number, with the grain of eachsheet'in cross-wise relation to that of the adjacent sheets. The stackor pile of assembled sheets is then. subjected to heat and pressure,either in press or by being passed through heated rolls, and maintainedin such heat and pressure from one and onehalf to five minutes. A heatof from 90 degrees C. to 120 degrees C. is sufficient.

After the step of pressing under heat the composite board or panel isready for use,

no further drying being necessary, or it may be shipped or storedready'for shipment, as may be desired.

It is to be noted that in moistening the surface of the sheetspreparatory to the application of the dry glue thereto, if a 1% cansticsoda solution is used instead of water, a much better result is attainedas the caustic soda solution will react with the glue powder to impartto the latter a greater adhesive or binding power. This constitutes avaluable feature of my invention. I

Second, when synthetic resins, or the mixture of synthetic and naturalresins, or the mixture of synthetic resins and proteidal substances areemployed as the dry glue product, the wood sheets are prepared in thesame way as above described.

For an example, 100 pounds of phenol are mixed with an equal weight offormaldehyde solution and a few pounds of catalyzing agent such asammonia or caustic soda added. \Vith the resulting phenolic oily massfrom 10 to 20 pounds of natural gums, such as shellac or dammergum aremixed, and finally from 30 to 100 pounds of soya bean meal, or otherproteidal substance, are added. The mass is then thoroughly mixed into adry powder which is ready for use as a dry glue product in accordancewith my inventlon. In this case natural resins, while imparting adhesivepower to the glue product, are not always necessary, whereas theproteidal material is necessary, otherwise the heat of the hot press orrolls would liquefy the synthetic resin which, in liquid form, would beabsorbed into the tissue of the wood sheets, thereby losing its adhesivepower. The use of a proteidal substance therefore, in this example, is amost important feature of my invention and its omission by others whohave worked on the problem marks the real cause of their failure toattain success.

The remaining operations are the same as above described except that inthis instance a minimum amount of dilute caustic soda solution should beused in dampening this surface. of the wood sheets.

The resulting composite board or panel, in this instance, is much morewaterproof and is stronger than in the first example above given.

It is not necessary for the synthetic resin and the proteidal substancesto be mixed together. These substances may be applied separately to thewood sheets. In this case the proteidal glue product is formed into apaste by mixing the same with water, and this paste is first applied tothe surface of the wood sheets, as little as possible of the paste beingemployed, just suflicient to fill up the wood tissue pores to preventabsorption of the resins. The synthetic resin, diluted to a thin liquidis then applied. Instead of organic solvents for the resins, such asalcohol,

amyl-alcohol, or amyl-acetate, I pitefer to use a caustic soda solutionfor this purpose, as

well as to thin the liquid resin. This results in imparting an increasedbinding power to the glue product. It is necessary to em loy 100 to 150pounds of the caustic soda 0 ten per cent solution with 100 pounds ofoily synthetic resin. Not only does the proteidal substance employed inthis case fill up the pores of the wood and prevent absorption of theresinous constituent into the wood, but it also reacts chemically withthe synthetic resin to impart an enhanced binding power. Not only thisbut the setting of the glue is accomplished quicker and at a lowertemperature. In place of the glue product hereinbefore described, myinvention may also utilize the lacquer product set forth in my PatentNo. 1,245,981, granted November 6, 1917. In the use of the glue-likemass therein described, said mass is diluted with a suitable solvent,such as alcohol, benzol, acetone and the like, or diluted caustic sodasolution may be used. The diluted mass is then applied to the woodsheets which are then air dried. When a pile of assembled sheets orpanels thus treated is subjected to pressure and heat the lacquergluebecomes thermoplastic and possesses a strongly adhesive property.Instead of first adding phenol to the proteid to glutinize it, and thenadding formaldehyde as a condensing agent, to obtain the glue-like mass,the glutinizer and the condensing agent may be mixed together and .thenthe proteid glutinized by means of caustic soda as a dissolving binderagent. The mixed 'glutinizing and condensing agents are preferablyheated thereby obtaining an oily viscous synthetic resin. In this formit is added to the diluted proteidal material.

If desired, the varnish product of my Patent No. 1,280,861, granted Oct.8, 1918, may be used as the adhesive agent in carrying out my presentinvention, being applied to the wood sheets which are then air dried andpressed together under heat which renders the varnish thermoplastic withexcellent adhesive properties. 1

Instead of applying the glue product, whether in the dry, powdered,semi-plastic, lacquer or varnish form, directly to the woodboards orpanels it may be first applied to a thin sheet of paper, cloth or othersuitable carrier, which is then dried and applied to or placed betweenthe sheets of board or panels and the whole assembly pressed togetherun-' der heat. In this method of utilizing my invention, theconstituents of the adhesive are not absorbed by the fibres of the boardsheets, thereby avoiding an objection sometimes encountered in applyingthe adhesive directly to the wood panel surface, particularly where theadhesive is more or less liquid.

From the foregoing description, it will be seen that I have provided acomposite board no I structure which is better, more strongly adhesiveand waterproof to a higher degree than has ever been accomplishedbefore, and a process of producing the same by the use of a dry glueproduct which is exceedingly simple, eflicient and inexpensive.

'Having now set forth the objects and na-.

faces of thin sheets of wood a dry thermoplastic glue comprising aproteidal product indurated with a methylene compound and possessinghigh binding and waterproofing qualities, stacking said sheets the oneupon another, and applying heat and pressure to the stack.

2. The process of forming composite boards which consists in applying tothe surfaces of thin sheets of wood, containing at least 10% ofmoisture, a dry thermoplastic glue containing proteidal and condensationproducts and possessing adhesive and waterproofing qualities, stackingsaid sheets upon each other, and applying heat and pressure to thestack.

3. The process of forming composite boards which consists iii-dampeningwith a caustic soda solution the surfaces of thin sheets of wood, thenapplying in the dry state a thermoplastic glue containing a proteidmixed with a condensation product to the dampened surfaces, thenstacking the sheets upon each other, and applying heat and pressure tothe stack.

4. The process which consists in dampening the surfaces of thin woodsheets and applying thereto a layer of dry thermoplastic glue containinga proteid material and a phenol condensation product, then stacking thesheets upon each other and applying heat and pressure to the stack.

5. The process which consists in applying to the surfaces of thin woodsheets a dry thermoplastic glue containing a proteid and a condensationproduct, then stacking the sheets upon each other. and applying heat andpressure to the stack.

6. The process which consists in applying to the surfaces of thin woodsheets a dry thermoplastic glue containing a proteid and a phenoliccondensation product, then stacking the sheets upon each other, andapplying heat and pressure to the stack.

7. The process which consists in applying a proteidal substance to thesurfaces of thin sheets of Wood, then applying a phenolic condensationproduct thereto, then stacking the sheets and applying heat and pressureto the stack.

8. The process s'wh-ichconsists in applying in a dry state a yntheticresin and a proteidal substance to the surfaces of thin sheets of wood,then stacking the sheets and applyinkheat and pressure to the stack.

9. That to the surface of thin sheets of wood an adhesive of athermoplastic nature containing proteidal substances and a methyleneinduratlng compound,.then assembling the sheets into a stack andapplying heat and pressure to the assembled stack.

. 10. As a new article ofmanufacture, a composite board composed of aplurality of thin sheets of wood superposed upon each other and unitedby an indurated proteidal glue product applied dry as a surface layerand having thermoplastic properties.

11. As a new article of manufacture, a composite board comprising aplurality of thin sheets piled one, upon another and joined by a thinlayer of indurated waterproofing proteid adhesive applied dry and havingthermoplastic, properties, said sheets being pressed together underheat.

12. The process of forming composite boards which consists in applyingto the surfaces of thin sheets of wood a dry glue comprising proteidaland condensation products and having thermoplastic adhesive andwaterproofing characteristics, stacking said sheets one upon another andapplying heat and pressure to the stack.

13. The process which consists in applying an adhesive having athermoplastic nature and containing proteidal substances, and amethylene induration compound to the surfaces of thin sheets of Wood,then assembling the sheets into a stack and applying heat and pressureto the assembled stack.

In testimony whereof I have hereunto set my hand on this 10th day ofApril A. D.,

TEIKICHI SATOW.

process which: consists in applying

